Conventionally, for gasoline automobiles, a wire harness (or a battery cable) or the like for pressure-bonding and thus connecting a tin-plated copper terminal and a copper electric wire to each other is used. Since carbon dioxide emissions from automobiles are required to be reduced today, electric automobiles or hybrid automobiles using more wire harnesses than the gasoline automobiles are in a wider use.
For all the types of automobiles including gasoline automobiles, weight reduction of a vehicle significantly influences the fuel efficiency. In an attempt to reduce the weight, aluminum (or aluminum alloy) electric wires are used for the wire harnesses, battery cables and the like, as well as copper (or copper alloy) electric wires.
However, in the case where an aluminum electric wire formed of aluminum or an aluminum alloy is pressure-bonded and thus connected to a crimp terminal formed of copper or a copper alloy, when there is moisture such as condensed dew, seawater or the like between the electric wire and the crimp terminal, an electrochemical reaction occurs. Specifically, a phenomenon called “galvanic corrosion” that aluminum or the aluminum alloy having a low potential is corroded by contact with a metal material having a high potential used to form the crimp terminal such as tin plating, gold plating, a copper alloy or the like occurs.
Due to the galvanic corrosion, the aluminum electric wire pressure-bonded by a pressure-bonding section of the terminal is corroded, dissolved or extinguished. This raises the electric resistance, and may prevent the electric wire from having a sufficient conducting function.
For a connection structural body in which such an aluminum electric wire formed of aluminum or an aluminum alloy is connected to a crimp terminal formed of copper, a copper alloy or the like, the following connection structure has been proposed in order to prevent galvanic corrosion of the aluminum electric wire. A part of the aluminum electric wire which is exposed as a result of being stripped of an insulating cover is inserted into a terminal having a bottom with holes into which molten solder has been injected. The exposed part of the aluminum electric wire is caulked via the solder and thus pressure-bonded to the terminal (see Patent Document 1).
Galvanic corrosion does not occur due to an aluminum electric wire and a crimp terminal formed of the same type of material. However, in the connection structure described in Patent Document 1, a part of the aluminum electric wire from a tip of the insulating cover to a position at which the electric wire is inserted into the terminal is exposed and is not water-proof. Therefore, in the case where the crimp terminal is formed of brass, copper or the like, which is used conventionally, or in the case where there is solder, galvanic corrosion is likely to occur in the contact part of the aluminum electric wire and the crimp terminal or the soldered part of the aluminum electric wire due to difference in the ionization tendency of the materials.
As another measure against galvanic corrosion of the aluminum electric wire, more specifically as a measure to prevent galvanic corrosion when the electric wire and the metal fittings of the crimp terminal are formed of different metal materials, the following connection structure has been proposed. A part of the aluminum electric wire which is exposed as a result of being stripped of an insulating cover is covered with an intermediate cap formed of the same type of copper alloy as that of the crimp terminal, and a caulking piece is caulked to enclose the intermediate cap, thus to pressure-bond and thus fix the aluminum electric wire to the crimp terminal (see Patent Document 2).
However, the connection structure described in Patent Document 2 is for use in thick electric wires such as, for example, electric wires for electric power used for electric automobiles, and is difficult to be applied to thin electric wires. This connection structure also requires many components such as special members, an intermediate cap of a specific shape, elastic members and the like, and the work of inserting the components is complicated. For these reasons, the connection structure described in Patent Document 2 is disadvantageous in terms of cost.